This invention is related to the use of catheter systems for treating certain conditions within the body of a patient and in particular the use of protective sheaths for covering parts of the catheter system while the system is being positioned within the patient's body.
A catheter system is used to deliver various therapeutic treatments to remote sites within a patient's body. A therapeutic device located near the distal end of the catheter system is positioned by advancing the catheter system through the tortuous curves of the patient's vasculature until the therapeutic device is in the proper position. An example of one such therapeutic device is an intravascular stent for holding open and maintaining the free passage of fluids in an artery or other vessel. A stent often may be deployed following a percutaneous transluminal coronary angioplasty (PTCA). In a PTCA procedure, a guiding catheter having a preformed distal tip is precutaneously introduced into the cardiovascular system of the patient in a conventional Seldinger technique and advanced within the cardiovascular system until the distal tip of the guiding catheter is seated at the ostium of a desired coronary artery. A guide wire is positioned within an inner lumen of a dilatation catheter having an inflatable balloon on the distal and both the catheter and guide wire are advanced through the previously placed guiding catheter to its distal end. The guide wire is first advanced out of the distal end of the guiding catheter and into the vasculature of the patient until the distal end of the guide wire crosses the lesion to be dilated. The dilatation catheter, with its distally mounted balloon, is then advanced out of the distal end of the guiding catheter over the guide wire until the balloon is properly positioned to dilate the narrowed region. The balloon is then inflated with a radiopaque fluid to a predetermined size to dilate the artery in the stenotic region. The balloon is then deflated and the catheter removed leaving the newly dilated artery with increased blood flow. In some cases the inflation of the balloon during angioplasty causes a dissection of the arterial lining or generally weakens the arterial wall in the area where the balloon was inflated. When the balloon is deflated after such a dilation, blood can flow between the arterial wall and the dissected lining, constricting the flow passage or causing a section of the lining to be forced into the flow thereby partially or completely blocking the blood flow in the artery. A stent is often used to re-secure a dissected lining in the artery wall.
Stents are well known tubular devices which, when expanded, contact the walls of a body lumen and maintains an open passage through the lumen. A stent delivery system often consists of an elongated catheter with an inflatable balloon on the distal end with an expandable stent mounted tightly around the inflatable balloon. The catheter is advanced over the in-place guide wire and then through the guiding catheter, out the distal tip of the guiding catheter and then through the patient arterial system until the stent is located at the site of the dissected arterial lining. The balloon is inflated causing the stent to expand and force the arterial lining back into place. The stent is expanded into contact with the walls of the artery at the site of the dissection and remains in an expanded state and opposed to the artery wall, holding open the artery after the balloon is deflated and the catheter and balloon are withdrawn from the patient. In an alternative procedure, an angioplasty may be performed with a stent over the dilation balloon thereby dilating the artery and ensuring its patency with a stent in one procedure.
Several problems can occur during the insertion of the stent delivery system, or any other device attached to the distal end of a delivery catheter, into the patient. One problem is that the device may become damaged on the way to the treatment site. For example, a stent may become dislodged from the balloon. This occurs when the stent bumps into the walls of the artery as it travels through the tortuous anatomy of the patient's vasculature. A second related problem is damage to the walls of the body lumen due to abrasion by the device as it passes through the vasculature. For example, a stent which often has an open lattice-like structure may present a relatively rough surface, abrading the walls of the body lumen as it passes. A third problem encountered during the insertion of the catheter system is the difficulty in advancing the leading edge of the relatively blunt end of the device such as a balloon and stent assembly past stenosed regions of the patient's arteries and ultimately past the obstruction to be repaired. This can be especially difficult in arteries with calcified deposits.
Finally, there are situations when a delivery catheter needs to be removed without first delivering the device such as when a stent cannot be delivered because of an unpassable obstruction or other complication. In this situation, the delivery catheter must be withdrawn and the stent must pass back through the distal port of the guiding catheter. There is a potential danger that the stent will become dislodged as it traverses the distal port of the guiding catheter. It may be the case that the guiding catheter must also be withdrawn if an undeployed device such as an unexpanded stent is to be removed safely.
One solution to the problem of abrasion between the device to be delivered and the walls of the body lumen is to enclose the device or the entire distal end of the device delivery system in a protective cover or sheath.
The prior art discloses catheter systems with pre-attached sheaths, which are typically incorporated onto the catheter system when the catheter is manufactured. Several examples of these types of sheath systems can be found in U.S. Pat. No. 4,733,665 to Palmaz, U.S. Pat. No. 5,458,615 to Klemm et al., and U.S. Pat. No. 5,158,548 to Lau et al.
Additional reasons for using a sheath with the delivery catheter system can include the overall poor condition of the patient's vasculature and where there is an increased risk of damage or embolism. Additionally, unexpected obstructions encountered during the dilation phase of the PTCA may, in the opinion of the physician, warrant the use of a sheath.
While there are several reasons that warrant use of a sheath to cover a device such as a stent, there also are factors which mitigate against using a sheath. One such factor is the additional time required to retract or remove the sheath from the device to be deployed. This is important when the physician wishes to minimize the time an artery is blocked by the device and where the size of the device is large relative to the size of the vessel. Another factor is that the addition of a sheath may make the overall outer diameter of the catheter too large to safely reach the treatment site. Another situation where the added complexity of using a sheath may not be warranted is when the blockage in the patient's artery is very close to the distal end of the guiding catheter so that the distance the delivery catheter must travel through the arteries is small. Here the opportunity for damage to either the device to be delivered or the walls of the patient's vasculature may be minimal.
As indicated above, some catheter systems include sheaths when they are manufactured so that the physician has no choice but to use the sheath, even if the application does not require the added protection provided by the sheath or warrant the added complexity.
What has been needed and heretofore unavailable is a sheath with a low profile to aid in catheter insertion which may be selected and added to a catheter system by the physician based on the condition encountered, thereby allowing the flexibility of using a sheath with a variety of catheter systems not originally designed to use a sheath.